chore: v2.8.7 — Git SSH keys in tabs, safer Artifacts preview and search

- Settings → Git → Your git identity: SSH keys are one tab per host kind
  (GitHub · GitLab, AWS CodeCommit, More keys, Other hosts); opens on the
  AWS tab when only an RSA key exists.
- Artifacts: a file type the sandboxed preview cannot show (Office, zip,
  PDF) offers Download only, never a blank Preview.
- Artifacts search: `%`/`_`/`\` in a query match literally (LIKE ... ESCAPE).
- Skill frontmatter rewrite replaces a key with its continuation lines and
  quotes values YAML could misread.
- Plugin marketplace.json is read with a 1 MB streaming cap.
- Artifact lists look each owner up once.

docs/plans/artifacts/README.md

@@ -19,7 +19,7 @@ One place to keep what agents PRODUCE, and (in server mode) to share it:
 ## Rules (binding, same spirit as CLAUDE.md)
 
 - **What is shared is a SNAPSHOT, never the owner's live file.** Sharing a `file`/`skill` copies it (size-capped, regular files only, no symlinks followed) into `<data dir>/artifacts/<id>/`, written once like `session_snapshots`. Viewers read only that copy, so no route ever reads another user's home for them. Re-sharing makes a new snapshot.
-- **Nothing shared runs on the dashboard's origin.** HTML/SVG previews are served under the `/git/raw` headers (`sandbox` CSP + `nosniff`) and shown in a sandboxed iframe; a `page` is only a link out, accepted only as `https://claude.ai/…`.
+- **Nothing shared runs on the dashboard's origin.** HTML/SVG previews are served under the `/git/raw` headers (`sandbox` CSP + `nosniff`) and shown in a sandboxed iframe; a type that sandbox cannot show (Office files, zip, PDF — the sandbox blocks both a download and the PDF viewer) gets Download only, never a blank Preview. A `page` is only a link out, accepted only as `https://claude.ai/…`.
 - **Installing is the viewer's explicit click, into the viewer's own account only.** For a skill, the hub writes the snapshot's files into `~/.claude/skills/<name>/` of the VIEWER (S3: as their member, through `write-as`). It never overwrites an existing skill without `conflict: replace`, and the old one goes to the trash first. For a plugin, the hub runs `claude plugin marketplace add <source>` + `claude plugin install <name>@<market> --scope user` as the viewer (the `applyPluginBaseline` path). The marketplace source passes an allowlist (`owner/repo` or a `validateRemoteUrl` URL), and no argv comes from the request beyond those two validated values.
 - **Before installing, the dialog lists every file of the skill** (a skill may carry scripts that the viewer's agent will run). Every share, unshare and install is written to `audit_log`.
 - **Visibility follows ownership:** a developer sees their own artifacts plus shared ones; admin/analyst see per `scope.js`, like sessions. Unshare removes an artifact from the Hub but does not uninstall copies others already installed.